Method of blowing-in through blast pipes submerged in a metallic bath

ABSTRACT

A METALLIC BATH IS REFINED BY BLOWING OXYGEN INTO THE BATH BY SUBMERGED BLAST PIPES. A PRIMARY JET IS CENTERED IN EACH BLAST PIPE FOR A GAS CONTAINING DROPLETS IN SUSPEN: SION TO REDUCE OR SUPPRESS METALLIC OXIDE FUMES OTHERWISE PRODUCED IN THE BATH BY THE OXYGEN.

P. LEROY 1 7 METHOD OF BLOWING-IN THROUGH BLAST PIPES Aug. 27, 1974 SUBMERGED IN A HETALLIC BATH Flled July 18, 1972 United States Patent Gflice 3,832,161 Patented Aug. 27, 1974 3,832,161 METHOD OF BLOWING-IN THROUGH BLAST PIPES SUBMERGED IN A METALLIC BATH Pierre Leroy, Saint-Germain-en-Laye, France, asslgnor to Creusot-Loire, Paris, France Filed July 18, 1972, Ser. No. 272,878

Int. Cl. C21c 5/34 U.S. Cl. 75--60 8 Claims ABSTRACT OF THE DISCLOSURE A metallic bath is refined by blowing oxygen into the bath by submerged blast pipes. A primary jet is centered in each blast pipe for a gas containing droplets in suspension to reduce or suppress metallic oxide fumes otherwise produced in the bath by the oxygen.

The present invention refers to a method of blowing in an oxidizing gas which may be pure oxygen, through blast pipes submerged in a refining metal bath, this method having the aim of acting on the zone of oxidization and superheat, and in particular of reducing the red or brown iron oxide fumes or even of practically suppressing them, in the case of refinement of a bath of cast iron or steel.

The release of these iron oxide fumes presents two disadvantages:

(a) It pollutes the ambient atmosphere (b) It constitutes a loss of iron.

In the known methods of blowing-in through blast pipes submerged in a metallic bath, the release of these iron oxide fumes is produced in the traditional Bessemer or Thomas converters, weakly if they are blowing in ordinary air, but appreciably if they are blowing in air enriched with oxygen.

More recently methods of blowing in pure oxygen through the bottom of the converter have appeared, wear of the blast pipes being slowed down by peripheral injection of a protective fluid with a feed separate from the main jet; these methods also release abundant iron oxide fumes.

In the various types of blowing in through submerged blast pipes, a known means of reduction of the quantity of iron oxide fumes emitted consists in mixing with the oxidizing gas or with the oxygen of the main jet a coolant gas, preferably endothermically dissociated, such as water vapour. But experience proves that in that case, in order to reduce the iron oxide fumes in a satisfactory proportion from the twin aspect of atmospheric pollution and loss of iron, large quantities of coolant must be blown in mixed with the oxygen and the thermal balance of the conversion therefore becomes much less favourable.

If the foregoing solution is ruled out because of the disadvantage of the poor thermal balance and because of other attendant inconveniences, one is reduced to equiping the converter with a trapping and dust-extraction installation which represents a large investment.

The aim of the present invention is considerably to reduce or even to suppress the oxide fumes produced by blowing-in from blast pipes submerged in a refining metal bath.

To this end the present invention has as its object a method of blowing-in through blast pipes submerged in a metallic bath, characterized by the introduction into the centre of each blast pipe of a primary jet with a separate feed, composed of a fluid reducing or suppressing the metallic oxide fumes liable to be produced in the bath by the secondary jet of oxidizing gas, which surrounds the primary jet without mixing with it in the blast pipe.

In accordance with a particular characteristic of the present invention the oxide-fume-reducing primary fluid is an endothermically dissociated fluid such as water vapour or water or atomized water in suspension in a car rier gas, for example.

In accordance with another particular characteristic of the present invention the primary fluid which reduces the oxidefumes is a chemically reducing fluid, more especially a fluid containing carbon, such as fuel-oil, for example, onelse a fluidized solid fuel in suspension in water or in fuel-oil.

One of the main advantages of the invention is that the effect of reduction or suppression of red fumes is obtained with relatively small quantities of primary fluid. In fact on the one hand this primary jet acts in the very heart of the superheat zone caused by the secondary jet of oxidiz ing gas opposite the tip of the blast pipe, and on the other hand it exerts on this secondary jet downstream of the tip of the blast pipe a divergent effect and thus succeeds in enlarging the superheat zone and therefore in re- 'ducipg its maximum temperature by dilution of this zone in a greater volume of the bulk of the metallic bath.

Another advantage of the invention, only achieved if the primary fluid is chemically reducing, is that it exerts a reducing actionon the oxides contained in the superheat zone and that in the case where the reducing element is carbon supplied by the primary fluid the reaction of reduction of the oxides is endothermic. Thus in the case of hydrocarbons supplied, for example, by fuel-oil, the coolant effect at the heart of the superheat zone is caused on the one hand by the cracking of the hydrocarbon molemiles; and on the other hand by the endothermic reduction of "the oxides, such as oxides of iron and manganese, silica, etc., by the carbon which springs from the cracking, and this at the heart of the superheat zone, precisely where high temperature favours the reduction of the various oxides by the carbon.

The effect of the primary fluid is thus very marked; that is why the necessary quantities of this primary fluid are relatively small and spoil the thermal balance of the conversion less than known methods employing mixtures such as oxygen and water vapour, for example. So it is that in so-called Thomas phosphoric cast iron, refined by blowing in oxygen applied from the bottom up, the addition of coolant scrap-iron, besides the normal addition of lime, is (fora 20-ton converter):

kg. per ton of melt for the blowing-in of a mixture of equal volumes of oxygen and water vapour through single-feed Thomas converter blast pipes, and producing very little iron oxide fumes.

300 kg. per ton of melt for blowing-in, in accordance with .the invention, through scparate-triple-feed blast-pipes, producing very little iron oxide fumes, and comprising therefor a primary jet of fuel-oil, a secondary jet of pure oxygen, and a tertiary jet of fuel-oil.

450 kg. per ton of melt for blowing-in through doublefeed blast-pipes comprising a primary jet of pure oxygen and a secondary jet of fuel-oil and producing a great deal of iron oxide fumes.

The method in accordance with the invention is equally well applicable to Thomas converters blowing in ordinary airor enriched air through the medium of a windchest, as to converters of more recent types blowing in without a windchest and at much higher pressure by means of separate-double-feed blast-pipes having in the centre a jet of oxidizing gas and round the periphery a jet of a fluid protective of the tip of the blast-pipe. It is sufficient in all cases to introduce on the axis of each blast pipe a supplementary tube of smaller diameter than the tube which surrounds it, and to feed it separately with special fluid intended to reduce or suppress the iron oxide fumes.

n the other hand the method in accordance with the invention is as well applicable to blast pipes situated in the bottom of the converter as to blast pipes placed in the lining at the sides and blowing either obliquely or horizontally below the surface of the bath. At a pinch certain of them can just as well be placed at the surface of the bath or even above this surface it it is considered useful in certain cases.

In order to make the invention fully understood an embodiment will be described below by way of non-restrictive example of the method in accordance with the invention for refinement of a steel melt by means of separate-triple-feed blast-pipes having a primary fuel-oil jet for diminishing or suppressing iron oxides fumes, a secondary pure oxygen jet for refinement, and a tertiary fueloil jet for protection of the tip of the blast pipe.

The single figure is a schematic vertical section through a blast pipe in accordance with this embodiment of the method.

The bottom plate 1 of cast iron or steel supports the refractory bottom 2. A massive ring-shaped piece 3 is attached to the plate 1 and receives the blast pipe comprising three concentric tubes 4, and 6.

The tube 4 is the pipe for primary fluid which is fueloil admitted at 7.

The tube 5 is the pipe for secondary fluid which is pure oxygen admitted at 8 and distributed by the part 9.

The tube 6 is the pipe for tertiary fluid which is fueloil admitted at 10 and distributed by the part 11.

At 12 an inspection hole enables access between operations to the central tube 4 and measuring of the length of blast pipe that remains by introducing a rod bent 'at the tip and scaled.

Of course all the circuits must be tight thanks to known means not illustrated in the single figure.

Relative to the feed of pure oxygen, the primary feed of fuel-oil which almost completely avoids iron oxide fumes is of the order of 75 grammes per Nm. of oxygen during desiliconizing and decarburizing of the Thomas melt when the carbon monoxide serves as vector gas for the volatilized iron. It falls to 40 and sometimes even 30 grammes per Nm. of oxygen during dephosphorizing. This primary feed is moreover adjustable at will, according to the appearance of the fumes at the mouth of the converter.

In parallel the tertiary feed of fuel-oil intended for protecting the tip of the blast pipe is set constant at about 35 grammes per Nm. of oxygen. This feed can be reduced very slightly if the blast pipe has a tendency to get partially blocked, and it can on the other hand be increased if the blast pipe tends to Wear away too quickly, which is checked from time to time via the access 12.

Of course one can without departing from the scope of the invention imagine variants and improvements in detail and also consider the use of equivalent means.

What is claimed is:

1. A method of blowing-in through blast pipes submerged in a metallic bath to be refined by means of an oxidizing gas, the steps of introducing into the center of each blast pipe a primary jet selected from the group consisting of a liquid and a gas containing droplets in suspension, reducing the metallic oxide fumes produced in the bath by a secondary jet of oxidizing gas surrounding said primary jet and preventing mixing of said jets in the blast pipe.

2. A method of blowing-in as in Claim 1, including the step of adding Water under pressure to the primary jet.

3. A method of blowing-in as in Claim 1, the primary jet being atomized water in suspension in a carrier gas.

4. A method of blowing-in as in Claim 1, the primary jet including a liquid having a chemically reducing action.

5. A method of blowing-in as in Claim 4, said liquid having a chemically reducing action providing carbon.

6. A method as is Claim 5, said liquid lbeing fuel-oil.

7. A method as in Claim 5, said liquid providing carbon being water holding a fluidized solid fuel in suspension.

8. A method as in Claim 5, said liquid providing carbon being fuel oil holding a fluidized solid fuel in suspension.

References Cited UNITED STATES PATENTS 3,330,645 7/1967 Moustier 60 3,706,549 12/1972 Knuppel 75-60 FOREIGN PATENTS 1,450,718 8/1966 France 7560 L. DEWAYNE RUTLEDGE, Primary Examiner P. D. ROSENBERG, Assistant Examiner F e v g ermmm m ci0mrJ-QtrI-0N5 Patent N 3,832,161 August 27, 1974 PIERRE LEROY Inventofls) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as sh wn below:

Foreign App'licatien Priority Data August. 4, 197a FRANCE '4. 71-28575 Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. 0. MARSHALL DANN Attesting Officer Commissioner of Patents 

